1. Field of the Invention
The invention relates to a means for sensing the relative movements of an object as set forth in the preamble of claim 1. The invention relates furthermore to possible applications of the means.
2. Prior Art
Known from DE 17 73 870 A1 is a load-sensitive transducer including a deformable intermediate piece disposed between two rigid flanges arranged longitudinally axial, the intermediate piece having the shape of a solid or hollow cylinder and comprising in its interior one or more load-sensitive elements, e.g. electrical strain gages producing a change in the electrical resistance as a function of the deformation of the intermediate piece caused by mechanical stress.
In one achieved embodiment four strain gages are contained in the solid cylindrical intermediate piece in two pairs in parallel, the strain gages of the one pair being arranged parallel to the direction of the exerted load, i.e. axially, whilst the strain gages of the other pair are arranged perpendicular to this direction. The strain gages of each pair are inserted in each diametrically opposed branch of an electric bridge circuit of a measurement device in each case for indicating the direct current of the bridge and thus the load exerted.
In another achieved embodiment only one or two electrical strain gages are inserted in a hollow cylindrical intermediate piece parallel to the exerted load, i.e. axially. In any case the load-sensitive elements, i.e. for example the strain gages are contained in the intermediate piece itself and thus incorporated therein so that the deformation caused by the mechanical stress can be accommodated at all in the intermediate piece.
To ensure that the electrical output values of the strain gages are practically independent of the spatial location of the strain gages in the intermediate piece in each case and that the exerted load is evenly distributed over the cross-section of the deformable intermediate piece, there is additionally inserted between each of the two flanges and the deformable intermediate piece a further body made of an elastomer material, e.g. rubber. The intention of this known arrangement is to measure the mechanical load exerted on the two flanges so that the indication achieved with the aid of the load-sensitive elements, i.e. e.g. the strain gage is substantially independent of the effective line of the load through the intermediate piece.
This known means permits sensing certain relative movements of an object and comprises an input flange securable to the object, a flange rigidly connected to a baseplate, and in the second achieved embodiment in addition a roughly ring-shaped intermediate piece arranged between the two flanges to which it is connected resistant to turning and shifting out of place and is made of an elastomer and including a force-sensing unit in its interior for sensing the movement of each flange relative to the other.
However, this known means permits sensing and measuring substantially only vertical relative movements of an object, but not any side or slanting relative movements and not at all any rotary excursion.
Known from DD 277 330 A1 is an ON/OFF force sensor including a rubber ring mounted on a baseplate, on which a cover plate is located exposed to a force from above as is to be measured. Applied to the inner circumference of the rubber ring, as a connecting part, is an open flexible ring, to the one end of which an electrical springer switch and to the other end of which a set screw is attached which urges the plunger of the springer switch.
Thus, the electrical springer switch is activated by the deformation of the rubber ring caused by the force acting thereon, resulting in a change in the diameter of the flexible ring. The circumference of the flexible ring is accordingly altered by roughly three times which makes for a higher reliability in the response of the springer switch. However, with this known force sensor only the vertical component of a force, i.e. a vertical relative movement of an object can be determined substantially. In this case too, this does not involve a force/moment sensor with which substantially a broad variety of relative movements can be sensed and measured as with the present invention.
Known from DE 39 40 696 C2 is a force sensor producing a practically linear electrical output signal as a function of the active force of the displacement to be sensed, wherein no change in the point at which the force is active occurs, but instead a lengthening of the sensor body in the direction in which the force is active. This force sensor has a folded-type structure and comprises in an effective partial range a mechanical electrical transducer element which is sensitive to the shortening of the surface of the transducer element when the sensor is exposed to tensile loading, this shortening being caused by the bending of the surface about an axis extending parallel to the direction in which the force is effective. This known force sensor too, responds substantially only to relative movement in one direction, in this case in the longitudinal direction of the force sensor.
Suitable for sensing a variety of relative movements are force/moment sensors as known for example from DE 36 11 336 C2 or EP 0 240 023 B1. With the aid of such a force/moment sensor linear displacements and/or rotary excursions can be sensed and converted for example directly into translational and rotational movements in thus permitting the control of automated machines, robotic manipulators or similar systems.
Both the force/moment sensors as cited above as well as all force/moment sensors currently on the market have only a relatively limited stiffness, or, in other words, no high forces or torques can be sensed and processed by these known force/moment sensors. In the case of robotic manipulators, for example, torques of a magnitude in the region of 100 Nm and more may occur at the welding tongs manipulated thereby. Such high torques cannot be sensed and/or processed by force/moment sensors currently available, however.
It is thus the objective of the invention to provide a means in making use of a force/moment sensor with which the relative movements of objects, especially also of large and correspondingly heavy objects, can be sensed. The intention is to permit sensing and measuring a wide variety of relative movements of an object so that the results can then be analyzed and more particularly made use of for precisely controlling and monitoring the momentary location of the object even when the objects involved are very large and heavy.
In accordance with the invention this objective is achieved by the features in the characterizing clause relating to a means as set forth in the preamble of claim 1. Advantageous further embodiments and possible applications of the invention are the subject matter of the sub-claims.
Unlike the embodiment of the invention in which the cap of the sensing unit, provided in the internal portion of the intermediate part, is secured to the force/moment sensor in the middle of the input flange to thus totally sense and transduce the translational and rotational movements, in the other embodiment in which the sensing unit with its cap is secured to a connecting part provided in the middle portion of the roughly ring-shaped intermediate part and protruding into the interior thereof, only approximately half of the translational and rotational values are available in each case for analysis.
In accordance with one advantageous aspect of the invention the multiple-piece intermediate part may be formed of approximately ring-shaped sections of approximately rectangular cross-section or also of approximately circularly arranged cuboidal elements. Furthermore, the multiple-piece intermediate part may also be configured of cylindrical elements arranged approximately circularly with a square, rectangular, polygonal and/or circular cross-section.
In accordance with another advantageous aspect of the invention both the approximately circularly configured one-piece intermediate part and the approximately ring-shaped multiple-piece intermediate part consisting of the same and/or different elements may contain same and/or differingly dimensioned webs and/or also struts preferably arranged like a trussed structure. In addition, the elements of a multiple-piece intermediate part may also be configured as a hollow body having a cross and/or criss-cross type structure.
With the means in accordance with the invention when making use of force/moment sensors as known, for example, from U.S. Pat. No. 4,763,531 or U.S. Pat. No. 4,785,180 with which, for example, translational displacements in the magnitude of maximally xc2x11.5 mm or rotational movements in the magnitude of a few angular degrees can be sensed, relative movements prompted also by objects weighing less than a kilopond (kp) up to several hundred tons (t) can now be sensed and thus ultimately measured depending on the size and design of the intermediate part produced of elastomer or cast resin.
For example, in checking the vertical orientation of a crane or to sense impending tilt or elevation movements, the crane can be mounted on a correspondingly dimensioned platform under which means numbering three, four or more in accordance with the invention are arranged whose intermediate elements are adequately dimensioned in accordance with the anticipated loads and stresses.
With such an array of means configured in accordance with the invention under the platform on which the crane is mounted, even the slightest departure from the vertical and thus also any impending elevation angle can be instantly sensed without any difficulty so that countermeasures as may be needed can be instigated in due time. In this way, it is thus possible, for example, to also avoid buckling of a load crane.
Instead of a crane, it is just as possible to mount on a correspondingly dimensioned platform a robotic device, a machine tool as well as any machine correspondingly designed in function and configuration. Yet another possible application of the means in accordance with the invention consists of attaching it, for example, to the end of a robotic arm and, for example, a holding or gripping device manipulated by the robotic device.
Furthermore, the means in accordance with the invention may also be put to use to advantage in vehicle final assembly, by at least one of the means in accordance with the invention being provided in each case in or on pins of racks on which frames are positioned to which in turn further frame and/or body parts of a vehicle in production are secured, for example, by means of welding tongs.
As soon as a first spot is set via the welding tongs controlled by the robotic device, a force or pressure is exerted thereby on the rack, it being at this moment that six possible degrees of freedom are sensed and measured by each sensor of the means in accordance with the invention provided in or on the pins.
This means that when, for example, four force/moment sensors are provided on or in four different pins of the rack, (4xc3x976) degrees of freedom materialize, i.e. 24 so-called input neuroses can be xe2x80x9ctrainedxe2x80x9d which can be analyzed to precisely determine where the first weld spot has been set.
When the next, i.e. second welding spot is made, it can thus be assured in this way that it is correctly set. Making use of the means in accordance with the invention or the force/moment sensors provided therein thus permits absolute positioning accuracy to be produced between robotic device and frame, resulting in all further welding spots being set with high accuracy.
The same result is achievable when means in accordance with the invention are placed under a robotic device to thus permit measuring a force exerted by the robotic device as a reaction force whilst precisely determining the location at which the exerted force has been applied. Accordingly, it is not mandatory that the means in accordance with the invention is fitted in a robotic joint, instead, as already mentioned above, the robotic device can be mounted on a correspondingly dimensioned platform under which a number of, for example, three, four or more means are arranged, each provided with a force/moment sensor.
The means in accordance with the invention may also find application in the security area of a bank, for example. In this case a number of means in accordance with the invention including force/moment sensors are arranged under a correspondingly dimensioned gangplate. Anybody walking over such a plate xe2x80x9cpreparedxe2x80x9d as described above leaves a trail of xe2x80x9cfootprintsxe2x80x9d which in sequence and gait is just as unique as, for example, a fingerprint for the person concerned in being precisely recorded for identification.